The trivial problem of weight painting and x symmetry
There are 2 different kinds of symmetry in weight paint:
n. 1 is for &quot;center&quot; bones, where every stroke on the left part of the mesh will be copied on the right side (in the same vertex group).
n. 2 is for couples of bones .L and .R, where a stroke on the .L vertex group will result in a similar mirrored stroke ond the corresponding .R vertex group.
Theese 2 options are not intended to be used together, you have to enable and disable them according to the selected bone/vertex group.